1. Field of the Invention
This invention relates to a patterned substrate and a light-emitting diode having the patterned substrate.
2. Description of the Related Art
A light-emitting diode (LED) has been widely used in a backlight module of a display, a traffic light, a lighting equipment, etc. When the LED serves as a light source for illumination or for supplying optical energy, a sufficient luminance is one of the basic requirements for the LED.
Therefore, in order to solve the problem of insufficient luminance of the LED, the inventors of this application had proposed a light-emitting element that is disclosed in Taiwan patent no. 1236773. Referring to FIGS. 1 and 2, the light-emitting element includes a substrate 11 that is primarily made of sapphire, an epitaxial layer unit 12 formed on the substrate 11, a Ti/Al/Ti/Au contact electrode 13, and a Ni/Au contact electrode 14.
The substrate 11 is patterned, and has a top surface 111, and a plurality of recesses 112 that are indented downwardly from the top surface 111 and that are spaced apart from each other. Each of the recesses 112 has a depth of 1.5 microns, and a bottom wall face having a diameter of 3 microns. A center-to-center distance between adjacent ones of the recesses is greater than 3 microns (for example, 5 microns).
The epitaxial layer unit 12 primarily made of a GaN material is formed on the top surface 111 of the substrate 11 and fills the recesses 112. The epitaxial layer unit 12 includes, from bottom to top, an n-type semiconductor layer 121 that is formed on the top surface 111 of the substrate 11 and that fills the recesses 112, a light-emitting layer 122 that partially covers the n-type semiconductor layer 121 and that is capable of emitting light with a predetermined range of wavelength, and a p-type semiconductor layer 123 covering the light-emitting layer 122.
The Ti/Al/Ti/Au contact electrode 13 and the Ni/Au contact electrode 14 are respectively disposed on the n-type semiconductor layer 121 and the p-type semiconductor layer 123, and are used to supply electricity to the epitaxial layer unit 12.
After external electricity is applied to the Ti/Al/Ti/Au contact electrode 13 and the Ni/Au contact electrode 14, the electricity flows to the n-type semiconductor layer 121, the p-type semiconductor layer 123, and the light-emitting layer 122, and is converted to optical energy to emit light outwardly.
When the light from the light-emitting layer 122 toward the substrate 11 travels to the top surface 111 and the recesses 112 of the substrate 11, the light can be reflected by the top surface 111 and the recesses 112 more than one time. Accordingly, the luminance of the light-emitting element is higher than that of a light-emitting element without a patterned substrate.
On the other hand, the recesses 112 may efficiently reduce defects and dislocation of the epitaxial layer unit 12. Therefore, an internal quantum efficiency of the light-emitting element may be enhanced, thereby resulting in an increase in luminance of the light-emitting element.
Because the patterned substrate 11 may efficiently improve the quality of the epitaxial layer unit 12 and may vary a traveling pathway of the light, studies to further enhance the luminance of the light-emitting element by varying patterns on the substrate 11 are continuously ongoing.